I only want to suggest you that don’t work for whole hardware, the only main things which people consider to get upgraded is the camera, the ram and the storage options. So work on this things and the OS part is totally differ, after finishing the hardware task move on SW. It will be great for you if you achieve what you mentioned. My blessings are always with you!

I have searched the google for smartphone parts but not satisfied result are coming. I m thinking about using the parts of old smartphones that are not in use but some parts are useful. i have to do some little research about its compatibility.